1. Field of the Invention
The present invention concerns a variable resistor requiring a long operation life.
2. Description of the Prior Art
Variable resistors generally have a basic structure in which a slider is caused to slide on a resistor body, and an operation life as long as several millions of cycles is sometimes required depending on application uses. The present applicant has previously developed a variable resistor as disclosed in U.S. patent application Ser. No. 652,940. This resistor contains carbon fibers in a film of the resistor body in which the carbon fibers protrude out of the surface of the resistor film and a slide contact is adapted to slide on the carbon fibers. Since the carbon fibers are hard, they are scarcely abraded by the sliding movement of the slider. Accordingly, this resistor is free from drawbacks of resistor bodies in the prior art not containing the carbon fibers but containing only carbon black or graphite in which a resistance film is abraded due to the sliding movement of the slider to result in change of the resistance value of the resistor body, or sliding noises are caused due to presence of abraded powder at the boundary between the resistor body and the slider and, as a result, the proposed resistor can provide a long operation life.
However, in the variable resistor invented by the present applicant as described above, since the hardness of the carbon fibers is greater than that of the slider, it involves a problem that the slider is abraded to such an extent as capable of attaining the function no more and, as a result, gives a problem that no sufficient operation life can be provided for the market demand.